Endorphins are ligands of the opioid receptors that regulate the pain perception, and are responsible for the sense of euphoria. Endorphins are produced by the anterior pituitary gland in response to the delicious food (especially spicy food), sex, physical activity and as a part of the maternal behavior [1]. Endorphins are neuropeptides — small protein neurotransmitters that can contain from from five to a couple of dozens amino acids.

These molecules were first detected in the porcine brain and have been called endogenous morphines since they cause a similar effect on the body. However the structure of opiates (small non-protein drugs present in the milky juice of the opium poppy) is completely different. Interaction between endorphins and their receptors triggers a cascade of reactions that result in decreased release of tachykinins and substance P — the main mediators of pain [2].

Endorphins are released during an intensive laughter, which is the reason why the chronic pain can become weaker for laughing people [3]. Natural analgesia during secretion of endorphins underlies a number of non-standard therapeutic techniques, including pet-therapy or acupuncture [4, 5]. The role of the endorphins secretion is discussed in the context of the placebo effect and meditation mechanisms [6, 7].

Synthesis of the endorphins in response to exercise leads to the special kind of euphoria, the so called runner’s high [8]. There is a hypothesis that for this reason physical activity can help fight depression and anxiety disorders [9]. However, there is also a chance to develop a sort of an addiction to sports [10].

Excess of endorphins in childhood and their high level later on may be associated with autism. Currently the opioid antagonists are considered as a possible therapy for these kind of disorders [11].

Endorphin types and precursors

Human organism produces alpha, beta, gamma and sigma endorphins, as well as met-enkephalin that also belongs to this class of compounds. These peptides are from 5 to 31 amino acids in length and are synthesized from larger precursor proteins, such as pro-opiomelanocortin [12]. In addition to endorphins this precursor produces other bioactive peptides such as melanocyte-stimulating hormone, and adrenocorticotropin. Some peptides that come with food are also able to interact with opioid receptors. This is demonstrated by casomorphin (a product of milk casein breakdown), gluten exorphin and soymorphin from soybeans [13, 14].

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